HexUtils.java

package com.firefly.utils.codec;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.util.BitSet;

abstract public class HexUtils {
	
	/**
	 * Converts a byte array into a string of lower case hex chars.
	 * 
	 * @param bs
	 *            A byte array
	 * @param off
	 *            The index of the first byte to read
	 * @param length
	 *            The number of bytes to read.
	 * @return the string of hex chars.
	 */
	public static final String bytesToHex(byte[] bs, int off, int length) {
		if (bs.length <= off || bs.length < off + length)
			throw new IllegalArgumentException();
		StringBuilder sb = new StringBuilder(length * 2);
		bytesToHexAppend(bs, off, length, sb);
		return sb.toString();
	}

	public static final void bytesToHexAppend(byte[] bs, int off, int length,
			StringBuilder sb) {
		if (bs.length <= off || bs.length < off + length)
			throw new IllegalArgumentException();
		sb.ensureCapacity(sb.length() + length * 2);
		for (int i = off; i < (off + length); i++) {
			sb.append(Character.forDigit((bs[i] >>> 4) & 0xf, 16));
			sb.append(Character.forDigit(bs[i] & 0xf, 16));
		}
	}

	public static final String bytesToHex(byte[] bs) {
		return bytesToHex(bs, 0, bs.length);
	}

	public static final byte[] hexToBytes(String s) {
		return hexToBytes(s, 0);
	}

	public static final byte[] hexToBytes(String s, int off) {
		byte[] bs = new byte[off + (1 + s.length()) / 2];
		hexToBytes(s, bs, off);
		return bs;
	}

	/**
	 * Converts a String of hex characters into an array of bytes.
	 * 
	 * @param s
	 *            A string of hex characters (upper case or lower) of even
	 *            length.
	 * @param out
	 *            A byte array of length at least s.length()/2 + off
	 * @param off
	 *            The first byte to write of the array
	 */
	public static final void hexToBytes(String s, byte[] out, int off)
			throws NumberFormatException, IndexOutOfBoundsException {

		int slen = s.length();
		if ((slen % 2) != 0) {
			s = '0' + s;
		}

		if (out.length < off + slen / 2) {
			throw new IndexOutOfBoundsException(
					"Output buffer too small for input (" + out.length + '<'
							+ off + slen / 2 + ')');
		}

		// Safe to assume the string is even length
		byte b1, b2;
		for (int i = 0; i < slen; i += 2) {
			b1 = (byte) Character.digit(s.charAt(i), 16);
			b2 = (byte) Character.digit(s.charAt(i + 1), 16);
			if ((b1 < 0) || (b2 < 0)) {
				throw new NumberFormatException();
			}
			out[off + i / 2] = (byte) (b1 << 4 | b2);
		}
	}

	public final static byte[] bitsToBytes(BitSet ba, int size) {
		int bytesAlloc = countBytesForBits(size);
		byte[] b = new byte[bytesAlloc];

		for (int i = 0; i < b.length; i++) {
			short s = 0;
			for (int j = 0; j < 8; j++) {
				int idx = i * 8 + j;
				boolean val = idx > size - 1 ? false : ba.get(idx);
				s |= val ? (1 << j) : 0;
			}
			if (s > 255)
				throw new IllegalStateException("WTF? s = " + s);
			b[i] = (byte) s;
		}
		return b;
	}

	public final static String bitsToHexString(BitSet ba, int size) {
		return bytesToHex(bitsToBytes(ba, size));
	}

	public static int countBytesForBits(int size) {
		// Brackets matter here! == takes precedence over the rest
		return (size / 8) + ((size % 8) == 0 ? 0 : 1);
	}

	public static void bytesToBits(byte[] b, BitSet ba, int maxSize) {
		int x = 0;
		for (int i = 0; i < b.length; i++) {
			for (int j = 0; j < 8; j++) {
				if (x > maxSize)
					break;
				int mask = 1 << j;
				boolean value = (mask & b[i]) != 0;
				ba.set(x, value);
				x++;
			}
		}
	}

	/**
	 * Read a hex string of bits and write it into a bitset
	 * 
	 * @param s
	 *            hex string of the stored bits
	 * @param ba
	 *            the bitset to store the bits in
	 * @param length
	 *            the maximum number of bits to store
	 */
	public static void hexToBits(String s, BitSet ba, int length) {
		byte[] b = hexToBytes(s);
		bytesToBits(b, ba, length);
	}

	/**
	 * Write a (reasonably short) BigInteger to a stream.
	 * 
	 * @param integer
	 *            the BigInteger to write
	 * @param out
	 *            the stream to write it to
	 * @throws IOException
	 * 			I/O exception
	 */
	public static void writeBigInteger(BigInteger integer, DataOutputStream out)
			throws IOException {
		if (integer.signum() == -1) {
			throw new IllegalStateException("Negative BigInteger!");
		}
		byte[] buf = integer.toByteArray();
		if (buf.length > Short.MAX_VALUE)
			throw new IllegalStateException("Too long: " + buf.length);
		out.writeShort((short) buf.length);
		out.write(buf);
	}

	/**
	 * Read a (reasonably short) BigInteger from a DataInputStream
	 * 
	 * @param dis
	 *            the stream to read from
	 * @return a BigInteger
	 * 
	 * @throws IOException
	 * 			I/O exception
	 */
	public static BigInteger readBigInteger(DataInputStream dis)
			throws IOException {
		short i = dis.readShort();
		if (i < 0)
			throw new IOException("Invalid BigInteger length: " + i);
		byte[] buf = new byte[i];
		dis.readFully(buf);
		return new BigInteger(1, buf);
	}

	/**
	 * Turn a BigInteger into a hex string. BigInteger.toString(16) NPEs on Sun
	 * JDK 1.4.2_05.  The bugs in their Big* are getting seriously
	 * irritating...
	 * 
	 * @param bi
	 * 			a big integer.
	 * @return a hex string.
	 * 
	 */
	public static String biToHex(BigInteger bi) {
		return bytesToHex(bi.toByteArray());
	}
}